Method of studying earth formations employing carbon disulfide as a tracer



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l 'atented Dec. 11, 1951 UNITED STATES ATENT OFFICE METHGD OF STUDYING EARTH FORMA- TIONS EMPLOYING CARBON DISULFIDE AS A TRACER George G. Bernard and Michael Savoy, Chicago,

IlL, assignors to The Pure Oil Company, Chicago, Ill., a corporation of Ohio No Drawing. Application March 31, 1948, Serial No. 18,286

6 Claims. (01. 2s .2ee)

This invention relates to methods for secondary recovery of oil from earth formations andparticularly, it relates to a method for the determination'of earth porosity in the aid of secondary recovery.

It is common practice in oil fields to employ water to promote. flow of oil to wells becoming exhausted. This is carried out by pumping water under pressure into a dry well to force oil into adjacent formations for recovery from adv jacent wells. Another process employs air orgas to induce flow to unproductive wells. Es-

sentially, the methods are alike for they employ fluids to force the flow of oil into desired strata. In any secondary recovery method adopted, it is essential-that the operator know something about the earth formation in order to employ the recovery fluid to the greatest advantage. For example, knowledge of the direction, rate or extent of flow of injected fluids into an earth formation greatly facilitates the choice of a secondary recovery technique to be employed. This knowledge may be gained by tracer studies where-- in measurements are made of the amount of tracer and injected fluid forced into an earth formation per unit of time and the time of first appearance of the tracer in neighboring formations or the amounts of tracer and injected fluid appearing therein. From these measurements the flow characteristics of the formation maybe resolved. Accordingly, it is a fundamental object of our invention to provide a simple method of studying earth formations in order to permit operators to determine the nature of secondary recovery methods which should be adopted.

7 It is a second object of the invention to provide a method of studying earth formations which is simple enough for field use and within the skill of the ordinary oil field hand.

It is a third object of the invention to provide a method of following the course of injection fluid whether it be gas or liquid.

Other objects and advantages of the invention will in part be obvious and in part appear hereinafter.

.Our invention, accordingly, relates to an improved method for studying earth formations and for recovering oil retained in these formations by forcing it from the wells, which method involves injecting a fluid, such as a natural gas or water or other fluid which is not reactive with carbon disulfide under the conditions of use, into the earth formation including in the fluid about 1.0 per cent of carbon disulfide and determining the point. to .which the carbon disulfide penetrates.

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Information as to the tim of appearance of the first-detectibleamount of carbon disulfide tracer in the injected fluid arriving at remote points from the injection well is useful in estimating the rate and direction of migration of fluids in the formation and serves to confirm or augment results of previous core permeability determinations, electric log correlations, drilling records and bottom hole pressure studies relating to the establishment of the probable existence and location of crevices and fissures, faults or impermeable barriers within the formation treated. This formation is a valuable guide in adopting the most'economical and productive secondary recovering technique. If the fluid used is a gas, about 1.0 per cent of carbon disulfide vapor therein is adequate, although as little as one volume of carbon disulfide vapor in 400,000 volumes of injection gas can be used. If the fluid is water,.

it is preferred that it be substantially saturated with carbon disulfide. Because carbon disulfide does not occur naturally or with petroleum, its Y appearance at any point removed from the point of injection is an indication of direct conneci tion between that point and the point of injection. We have found that carbon disulfide vapor will permeate great distances through earth formations, although rather slowly, and will be retained in carrier fluid in detectable amounts.

Two principal virtues distinguish carbon disulflde as a tracer and methods characterized by the use of carbon disulfide as a tracer. The first is that it is a relatively reactive material, although not reactable with materials occurring in earth formations and, because of its reactivity, can be detected in small quantities in certain Well defined sensitive reactions. Its second virtue Where tracers,': such as helium are used, the costs can be prohibitive. vvsie tracers, such as a ggtyie ne are that it is quite safe to handle.

used, costs remain down, but explosion hazards are up. Carbon disulfide appears as the answer to both phases of the problem, because it is cheap and other organic sulfur compounds, but interference of these with the tests for carbon disulfide can readily be avoided as will be pointed out subsequently.

Where the injection fluid to be used is water or brine, it is advisable to employ a substantially saturated solution of carbon disulfide because at about ambient temperatures and pressures, carbon disulfldeis soluble in water to the extent of about 0.2 part by weight per hundred parts of water.

X Though it is detectable in much smaller concentrations; the course of the water through the earth formations can be more readily followed if reliance in the tracing thereof need not be placed upon thedetection of minute quantities'of carbon disulfide at test points.

Another advantage of using carbon disulfide as a tracer is one which rises out of what might at first appearance seem to be a disadvantage.

That is, its solubility in .hydrocarbon oils. When an :injection fluid containing carbon disulfide is forced .into an earth formation, its appearance direct communication between the point of injection and the point of test and, second, that in all probability, little or no oil exists in the earth vformation between the two points. This latter :conclusion is derived from the fact that since carbon disulfide is highly soluble in oil, it

would be scrubbed from the carrier fluid by any oil occurring in the formation. Thus, at test points, the appearance of the test fluid with or without the carbon disulfide tracer is of signiflcance which can be accurately interpreted.

The method of carrying out the study of an used. Twenty (20) days after cessation of the.

injection, the carbon disulfide was detected ina producing well 400 feet away from the injection well. There were test wells around that at which no carbon disulfide appeared, indicating as noted, the presence of oil :in the intermediate formation.

The-sampling of gas from the producing wells and the testing thereof for carbon disulfide was carried out by bubbling a sample of the injection gas recovered at a test point through a solution containing cupric acetate and diethylamine. The presence of carbon disulfide in'the gas was indicated by the development of a yellow coloration in the solution. Where the concentration of carbon disulfide vapor in the gas is low, the intensity of the coloration can be used as a semi- Water containing dissolved carbon disulfide can be used as an injection fluid and its appearance in test wells removed from the injection well interpreted to deduce information about the intermediate formation. When water is used as the injection fluid the volume ratio of water to carbon disulfide may be of the order of l to .5000. The technique parallels that when a gaseous injectionfluid is used.

quantitative or even quantitative estimate thereat test points will indicate, first,.that there is a The test for the carbon disulfide in the water recovered at the test point is the same as that used for the testing of carbon disulfide in the gas. We have found experimentally that carbon disulfide is detectable in quantities as small as one part in 400,000 of air and natural gases consisting of the common gaseous hydrocarbons. It is detectable also in aqueous and brine solutions in amounts as small as one part in 2,000,000.

The great solubility of carbon disulfide in oil and its moderate solubility in water are both turned to advantage in this process and the ease with which the carbon disulfide can be detected makes it possible to use it as a tracer in water injection operations because quite dilute solutions of the compound can be used. If it is lost in its course through the earth, a definite interpretation can be placed on the loss. Also, because it is detectable in minute concentrations, it is possible for it to pass through an earth formation, be partly absorbed in oil in the formation, and yet have a detectable quantity come through. Similar considerations apply to the use of carbon disulfide vapor intermixed with a gas as an injection fluid. 'Brines which occur in oil strata will dissolvecarbon disulfide, but to a considerably smaller extent than will pure water but, nevertheless, will give a positive indication of the presence of carbon disulfide in solutions containing as little as ,20 parts of carbon disulfide in 1,000,000 volumes of the brine.

.It is appar n to those skilled in the art that the above matter is merely illustrative and should not be construed as limiting the invention in any way, and thatchanges :may be made in'the process without departing from the spirit and scope of the invention.

What is claimed :is:

:1. The method of studying earth formations in the neighborhood .of an oil producing formation to determine their flow characteristics as an aid to the secondary recovery of .oil therefrom comprising, injecting into the formation a small amount of carbon disulfide and a fluid not reactive with carbon disulfide under the conditions of operation, withdrawing a sample of said fluid from the earth formation at a point removed from the :pointof injection and testing the fluid for the presence of carbon disulfide.

.2. The method of studying .earth formations in the neighborhood of an ;oil producing formation to determine their flow characteristics as an aid to the secondary recovery of oil therefrom com prising, injecting into the formation a fluid not reactive with carbon disulfide under the conditions of operation, the fluid containing a small amount of carbondisulfide, withdrawing a sample of said fluid from the earth formation at a point removed from the point of injection and testing the fluid for the presence of carbon disulfide.

3. The method in accordance with claim 2 in which the injected fluid is a gas containing about 0.001 to 1 volume .of carbon disulfide vapor per hundred volumes of gas.

4. The method in accordance with claim 2 in which the injected fluid is a natural gas containing about 0.001 .volume of carbon disulfide per hundred volumes of gas.

5. The method in accordance with claim 2 in which the injected fluid is water with .about '1 volume of carbon disulfide to one hundred to five thousand volumes of .water.

6. The method of studying .earth formations adjacent well bore to determine their flow characteristics as an aid to the secondary recovery 1 Age 5 of oil therefrom comprising. injecting to the said well bore water substantially saturated with carbon disulfide thereby to enter said formations, withdrawing samples of water from said formatlons at spaced points removed from said well I bore and testing such samples for the presence of carbon disulfide.

. GEORGE G. BERNARD.

MICHAEL SAVOY.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PAI'ENTS Number Name Date 2,348,985 Lewis May 16, 1944 OTHER REFERENCES Tischler, Ind. and Eng. Chem., Anal. Chem., vol. 4, page 146 (1932).

Frost, Helium Tracer Studies in The Elk Hills, Calif., Field, Bureau of Mines R. I. 3897. June 

1. THE METHOD OF STUDYING EARTH FORMATIONS IN THE NEIGHBORHOOD OF AN OIL PRODUCING FORMATION TO DETERMINE THIER FLOW CHARACTERISTICS AS AN AID TO THE SECONDARY RECOVERY OF OIL THEREFROM COMPRISING, INJECTING INTO THE FORMATION A SMALL AMOUNT OF CARBON DISULFIDE AND A FLUID NOT REACTIVE WITH CARBON DISULFIDE UNDER THE CONDITIONS OF OPERATION, WITHDRAWING A SAMPLE OF SAID FLUID FROM THE EARTH FORMATION AT A POINT REMOVED FROM THE POINT OF INJECTION AND TESTING THE FLUID FOR THE PRESENCE OF CARBON DISULFIDE. 